Mulberry (Molus alba L. and other plants of the genus Morus) has been cultivated in many Asian countries such as China, Korea, Japan and Thailand, and their leaves are used to feed silkworms (Bombyx mori L.). Additionally, the leaves are rich in alkaloid components including 1-deoxynojirimycin (1-DNJ) which is known as one of the most potent glucosidase inhibitors. Dietary mulberry 1-DNJ has been hypothesized to be beneficial for suppression of an abnormally high blood glucose level. In this study, we investigated the high 1-DNJ concentration cultivars from among over 500 various cultivars growing in the field at Experimental Farm of Shinshu University, to utilize the mulberry biomass in addition to feed silkworms. We extracted 1-DNJ from thirty-five varieties of mulberry leaves, and we determined the amount of 1-DNJ. As a result, some cultivars were found to contain a high DNJ concentration compared with Ichinose which is a standard cultivar.